棉酚致蛋鸡脂肪肝的分子机制

The rapid expansion of the livestock industry in the current world is resulting in the short availability of protein feed feedstuff, and cottonseed meal has been widely used as a feedstuff for protein feed for livestock. However, gossypol, as an ingredient of cottonseed meal, has been reported to exert several detrimental effects on laying hens, thus limits the application of cottonseed meal. According to the previous survey and investigation, laying hens exposed to a long-term feed containing gossypol showed significant increases in mortality rate and elimination rate, a symptom of fat liver and a damage in liver tissue and its subcellular structure, in the late growing period. The mechanism underlying gossypol inducing fat liver in laying hens is currently unknown. In the present study, laying hens will be chronically fed cottonseed meal to determine the pattern and quantity of the gossypol deposition in the liver, and the parameters will be then used to establish a model of laying hens with fat liver by an intravenous injection method. Using RT-PCR and Western blot, those key enzymes, gene regulators and hormones involved in the de novo lipogenesis, lipid assembly and delivery and lipid oxidation will be investigated in liver in vivo and in hapatocytes in vitro, as well as the histological changes and subcellular damages in hapatocytes. The study will be processed across the organismal, transcription and translation levels. The findings will provide a theory for cottonseed meal application in feed industry, ensuring laying hens healthy and productive.

在蛋白质饲料资源日益缺乏的今天，棉籽饼粕是一种比较理想的动物蛋白饲料来源，但是由于有害成分棉酚的存在，限制了其在蛋鸡生产中的应用。前期生产调研及研究发现，长期饲喂含棉酚饲料蛋鸡生产后期死淘率明显上升，脂肪肝程度显著加重，肝脏组织及亚细胞结构出现明显的损伤，但目前对棉酚如何导致蛋鸡脂肪肝的具体机制还不清楚。本项目将以蛋鸡为研究对象，利用长期饲喂棉粕日粮确定肝脏中棉酚的沉积规律和蓄积量，建立静脉注射棉酚技术构建蛋鸡脂肪肝模型，结合活体试验与肝细胞离体培养技术，借助RT-PCR技术和Western blot技术等，研究肝脏脂肪酸从头合成、脂肪组装与转运和脂肪氧化利用三个可能途径上的关键酶、关键调控因子和激素的变化，并结合肝细胞组织形态变化及亚细胞损伤程度分析，最终从肝脏组织水平、mRNA表达和蛋白水平综合确定棉酚致蛋鸡脂肪肝的分子机制，为更好的利用棉籽饼粕资源，保障蛋鸡健康和生产提供理论支持。

棉粕作为一种重要的蛋白质饲料资源，由于棉酚这一有毒物质的存在限制了其在畜禽饲料中的应用。生产中，蛋鸡长期饲喂含棉粕饲料后会出现生产后期死淘率上升和脂肪肝程度加重的现象，但造成这一现象的机制目前尚不清楚。本项目针对棉酚影响蛋鸡肝脏脂肪代谢的途径这一科学问题开展研究，通过棉粕饲喂蛋鸡生产试验、游离棉酚急性攻毒试验及体外肝细胞棉酚处理试验，开展了以下三个方面的研究工作：不同棉酚水平对蛋鸡生产性能的影响；棉酚对蛋鸡肝脏结构和功能的影响；棉酚对蛋鸡肝脏脂肪合成、转运和利用相关基因通路的影响。研究发现，蛋鸡长期饲喂含棉酚日粮导致棉酚在肝脏中的蓄积，引起肝脏损伤，降低蛋重，使蛋鸡的死淘率升高，而且棉酚蓄积毒性导致了蛋鸡肝脏脂肪代谢异常，其可能的机理在于棉酚引起脂肪酸从头生成的减少，而且这种减少作用源于SREBPs调控下的脂肪酸合成能力的改变，高棉酚水平抑制了肝脏中脂肪酸的β-氧化，降低了脂肪的利用，而且其调控途径可能并非通过PPARα途径，棉酚急性毒性造成蛋鸡肝脏脂肪合成和脂蛋白组装能力的加强，但脂蛋白的转运能力未产生改变。以上研究证明，棉酚在肝脏中蓄积引起蛋鸡肝脏功能损伤，影响其脂肪代谢，进而加重蛋鸡脂肪肝，造成生产后期蛋鸡死淘率升高和生产损失。